In storage devices that comply with standards, such as ATA (Advanced Technology Attachment) or SCSI (Small Computer System Interface), in general, there is a command called a force unit access (FUA) command that guarantees writing to a nonvolatile memory. Execution of the FUA command is finished when the information indicating completion of writing to the nonvolatile memory is reported from the nonvolatile memory to a controller.
However, where, for example, a plurality of commands are accumulated in a controller independently of data transfer, and are sequentially executed based on their tag numbers (as in Native command Queuing (NCQ) in the SATA (Serial-ATA) standard), if these commands are FUA commands that guarantee writing to a nonvolatile memory, the system may be degraded in performance.